Improvement on Potential Drifting for Sol–Gel and Electroplated Iridium Oxide-Based pH-Sensing Films

This letter investigates the use of external voltage resets to reduce drifting issues of iridium oxide (IrO
_x
) pH-sensing films. Two types of IrO
_x
films prepared by sol–gel and electroplating techniques were examined comparing hydrous and anhydrous material characteristics. The thin-film IrO
_x
allows inexpensive processing for flexible polyimide substrates enabling planar and monolithic integration for wearables and miniature pH sensors. Open-circuit potential drifts and external voltage resets were investigated for freshly prepared electrodes and retested after 14 days. External resets were examined at different voltage levels. Sol–gel electrodes showed 57% and 81% drift improvement in acid and alkaline test solutions, respectively, while electroplated ones showed 84% and 88% improvement. Sensitivity and hysteresis were investigated after external resets and showed promising results. A total of 15 sol–gel and 15 electroplated electrodes were characterized. Differences in pH characteristics are attributed to different types of IrO
_x
compositions. The quicker response transitions and reduced potential drifts will enable reliable long-term pH monitoring and reduce frequent calibration for pH-sensing applications.